Adding a + and - button in datagrid

Experts,

I have a texbox item in datagrid called Patches which is coming from a sql table and is a number.   I want to add a + and - buttons beside the patches textbox in the edittemplate of the datagrid,  I tried this way but it not displaying the buttons while editing each row.  The function for increasing and decreasing the number in the patches textbox are as follows, I tested by using these functions for +  and - buttons situated outside the datagrid they are working:

<script language="javascript">
               function Decrease()
               {
                    //alert(document.Form1
                    document.Form1.txtPatch.value = parseInt(document.Form1.txtPatch.value) - 1;
                    if (parseInt(document.Form1.txtPatch.value) < 0)
                         document.Form1.txtPatch.value = 0;
               }
               function Increase()
               {
                    //alert(document.Form1.txtPatch.value );
                    document.Form1.txtPatch.value = parseInt(document.Form1.txtPatch.value) + 1;
               }
</script>

PART NOT WORKING  :

<EditItemTemplate>

<ASP:TextBox id="txtPatch" Text='<%# Container.DataItem("Patches") %>' runat="server" /></asp:TextBox>
<asp:button id="butDecrease1" style="Z-INDEX: 106; LEFT: 592px; WIDTH: 96px; POSITION: absolute; TOP: 152px; HEIGHT: 24px"onclick="javascript:Decrease()"  > </asp:button>
<asp:button id="butIncrease1" style="Z-INDEX: 104; LEFT: 592px; WIDTH: 96px; POSITION: absolute; TOP: 112px; HEIGHT: 24px"onclick="javascript:Increase()" ></asp:button>

</EditItemTemplate>